1. Field of the Invention
The invention relates generally to blast noise measurement systems and particularly to a windscreen and vertical microphone configuration supported by the windscreen for eliminating wind noise interference.
2. Description of the Prior Art
Blast noise measurement and monitoring systems have previously been available and have utilized microphone arrangements for detection, measurement and monitoring of blast noise. Prior blast noise monitoring systems utilizing microphones for receiving acoustical data and processing the data have typically involved the horizontal spacing of microphone receivers. However, such prior systems suffer from the disadvantages that the acoustical signals arrive at the microphones at different times, thereby causing signal processing to be greatly complicated. Further, prior systems introduce inaccuracies into processed acoustical data since wind noise interference has not been successfully eliminated and the resulting acoustical data suffers from the inclusion of wind-generated pseudosound artifacts. Further difficulties inherent in a number of prior art systems involve the lack of portability of such systems, thereby rendering these systems less useful in the usual environmental noise measurement situation.
Examples of sound modifying structures useful with microphones and sound intensity measurement apparatus are provided in a number of issued United States patents. U.S. Pat. No. 3,550,720 to Ballard, a plurality of screens are disposed about a transducer in order to reduce the effect of wind on signals picked up by the transducer. Anderson et al in U.S. Pat. No. 2,520,706 provide a windscreen for use with a dual microphone arrangement, the windscreen being intended to reduce wind velocity incident on the microphones to prevent the generation of spurious sounds occasioned by wind flow but without appreciably attenuating soundwaves received by the microphones. In U.S. Pat. No. 4,236,040, Chung utilizes a pair of closely spaced microphones in a meter intended to measure sound intensity. Chung also provides a system for processing the output signals of the microphones.
Other United States patents which disclose examples of sound modifying structures useful with microphones are identified as follows:
U.S. Pat. No. 1,914,099--Bedell PA0 U.S. Pat. No. 2,263,408--Lakhovsky PA0 U.S. Pat. No. 2,200,097--Phelps PA0 U.S. Pat. No. 2,325,424--Rettinger PA0 U.S. Pat. No. 2,395,719--Bright PA0 U.S. Pat. No. 2,536,251--Caldwell, Jr. PA0 U.S. Pat. No. 2,623,957--Cragg et al PA0 U.S. Pat. No. 3,154,171--Knutson et al PA0 U.S. Pat. No. 3,265,153--Burroughs PA0 U.S. Pat. No. 3,515,240--Sugiyama et al
The prior art thus noted fails to provide a portable windscreen and microphone supporting system which is effective to reduce interference from wind-generated pseudosound and which is also acoustically transparent so as not to interfere with the reception of acoustical data by a pair of microphones which are vertically spaced from each other and mounted within the windscreen. The present invention thus provides a vertically spaced microphone configuration shielded by an arrangement of concentric windscreen cylinders which eliminates the problem of wind noise interference, particularly in the measurement and monitoring of low-frequency acoustic blast noise.